Polymeric materials are known which are effective for dispersing pigments in organic solvents and used to form pigment dispersions of uniform color that are useful in formulating water borne and solvent borne coating compositions. Such pigment dispersions are widely used, for example, in exterior coating for automobiles and trucks.
Much of the past activity concerning pigment dispersants has been with random copolymers, but such relatively inefficient materials are now being replaced by structured pigment dispersants, such as those described in US 2002/0137865 to BYK-Chemie GmbH. Graft copolymers are generally composed of a macromonomer grafted onto a polymer backbone and have attached to either the macromonomer, the backbone or both, one or more groups known as pigment anchoring groups which are designed to adsorb on the surface of a pigment particle and thereby anchor the polymer to the pigment surface.
While the past work indicates that graft copolymers are outstanding dispersants, the graft copolymers containing certain pigment anchoring groups can also suffer from certain significant drawbacks. For instance, the pigment anchoring groups may not selectively adsorb certain pigment types and/or can be displaced from pigment surfaces by polar solvents or other polar groups present in a coating composition. Ineffective anchoring of the dispersant to a pigment particle surface is highly undesired, since it can allow the pigment particles to flocculate, or cluster together, and can result, ultimately, in coatings of poor color quality.
Therefore, there is still a need to improve the performance of pigment dispersants, and in particular to find new graft copolymers that are more effective in dispersing a wide range of pigments, especially in coating compositions.